Inhibition of the serine protease HtrA1, which belongs to an evolutionarily conserved family of HtrA proteins, has the potential to protect and treat tissue damage caused by the degeneration of retinal or photoreceptor cells in the human eye. The pathophysiological relevance of HtrA1 in the progression of the age-related macular degeneration has been firmly established by human genetic studies where a SNP in the HtrA1 promoter region results in increased HtrA1 transcript and protein levels. Age-related macular degeneration is the leading cause of severe irreversible central vision loss and blindness in individuals over 65 years of age in developed countries. There are two forms of AMD: dry AMD and wet AMD. Wet AMD (also known as exudative AMD), is associated with pathologic posterior choroidal neovascularization subsequent to the disruption of the delimiting Bruch's membrane. Tissue edema due to the leakage from the abnormal blood vessels damages the macula and impairs vision, eventually leading to blindness. In dry AMD, drusen have been reported in the macula of the eye, the cells in the macula die for the progressive accumulation of the drusen, resulting in progressive vision loss. Dry AMD is clinically described to occur in three stages: 1) early, 2) intermediate, and 3) advanced dry AMD. Dry AMD can also progress into wet AMD during any stage of the disease. Treatment strategies for wet AMD exists and the current standard of care is Lucentis (Genentech/Roche) and Eylea (Regeneron), an anti-VEGF antibody and an anti-VEGF trap injected intravitreally respectively. There are no current treatments for preventing loss of vision for the dry form and for preventing progression of dry AMD to local atrophy of the retinal tissue. As discussed above, HtrA1 risk alleles have been associated, with high statistical significance, with the AMD onsets and the protein has been reported to be present in drusen. These studies and further evidences provide relevance that HtrA1 is a fundamental factor involved in the pathophysiology and progression in AMD. This concept is further confirmed in different AMD disease models, where increased HtrA1 protein levels in the retina tissue have been shown to be responsible for the degradation of extracellular matrix (ECM) proteins like fibronectin, fibulins and aggrecan. The physiological balance between production and disintegration of the ECM components allows for both creation and maintenance of proper retina tissue architecture. Such balance has been reported to be lost in the progression of the age-related macular degeneration. In particular, the fibulins (mainly-3, -5, -6) have been reported to be important components of the Bruch's membrane in maintaining the integrity of elastic lamina and organization of the retina tissue overall. Several variants in fibulin 5 and fibulin 3 were reported to be associated with AMD. Missense mutations of the fibulin 5 gene have been associated with reduced secretion of fibulin 5. Different studies have reported that Htra1 protease activity is directed to the cleavage of the fibulins as substrates. A direct inhibition of HtrA1 protease activity is expected to provide a protection reducing degradation of extracellular matrix proteins, in particular fibulins and fibrionectin, therefore preserving the retina tissue structure. The relevance of HtrA1's role in maintenance of the physiological homeostasis of the ECM components is firmly provided by the identification of human loss-of-function mutations causing familial ischemic cerebral small-vessel disease. The molecular mechanism underlies in the deficient TGFbeta inhibition by HtrA1 resulting in increased signaling levels, which in conjunction with deficient HtrA1-mediated degradation of various extracellular matrix components determine thickening of the intima responsible for the ischemic small-vessels. Given its fundamental role in regulating intracellular signaling pathways (e.g. TGFbeta) and the regulation of ECM proteins turnover, HtrA1 has been involved in several pathologies, as ocular diseases, rheumatoid arthritis, osteoarthritis, Alzheimer's disease, and some types of cancer.